1. Field of the Disclosure
The present disclosure relates to a backlight unit for a liquid crystal display (LCD) using a light emitting diode (LED), and more particularly, to a backlight unit for an LCD that employs a green light source with improved luminous efficiency.
2. Description of the Related Art
An LCD is a flat panel display (FPD) that is lightweight and consumes a small amount of power. However, the LCD is not a self-luminescent display but a light reception display for receiving light to form an image so that a user cannot distinguish the image in when in darkness. To solve this problem, a backlight unit is installed on a rear surface of the LCD.
A cold cathode fluorescent lamp (CCFL), which is a conventional backlight unit, has a fixed characteristic peak wavelength by gas discharge and exhibits low color purity owing to the noise wavelength of the LED.
To overcome the drawbacks of the CCFL, a backlight unit for an LCD using an LED is being investigated because the LED backlight unit makes emission wavelength and full width at half-maximum (FWHM) controllable and has not only very high color purity but also a good capacity for expressing color.
FIG. 1 is a graph showing internal quantum efficiency and extraction efficiency relative to peak wavelength.
Referring to FIG. 1, only a slight variation of extraction efficiency is shown in the entire wavelength range, but a very low internal quantum efficiency of 10% is shown in a green wavelength range of 500 to 600 nm. Therefore, a backlight unit for an LCD using a three-color LED needs green light sources in a number more than (e.g., twice as many as) the numbers of red light sources and blue light sources. This leads to a rise in power consumption and an increase in the cost of fabrication.
Meanwhile, light is emitted from a bandgap of an LED, and the bandgap is a function of temperature and current. Thus, a peak of emission wavelength may depend on the temperature and current of the LED. As a result, the LED emits unstable color of light according to variations in the temperature and current of the LED.